Figure 1: Simplified schematic representation of some intrathymic events that determine the developing T cell fate. In response to weak/moderate TCR signaling DP thymocytes can be induced to undergo maturation by the Ras pathway (left panel). The strong and prolonged interaction TCR/pMHC, with or without costimulatory molecules (represented by PD-1), will result in elimination of thymocytes by apoptosis (right panel). Thymocytes that fail to express a functional αβTCR cannot undergo maturation and they die due to lack of “survival signals” delivered throughout TCR (middle panel).